The present invention relates to metallurgy, and more particularly, to a method of treating pyrite bearing polymetallic material to obtain elemental sulphur, pyrrhotine concentrate to be subjected to further treatment with the purpose of removing the residual sulphur therefrom, and producing iron-ore pellets as well as the product enriched with nonferrous, rare and noble metals separated to form selective conditioned concentrates by any conventional technique.
This invention can find advantageous application in the treatment of pyrite bearing polymetallic material which includes non-ferrous, rare and noble metals.
There is known in the art a method of treating pyrite concentrate, which comprises heating (roasting) this material in the atmosphere of inert gas without air access, and then subjecting it to flash roasting at a temperature within the range of 1800.degree. C. to 2000.degree. C. Here, the pyrite concentrate, containing 46% by weight of iron and 52.8% by weight of sulphur, is subjected to thermal decomposition with the resultant formation of matte and separation of elemental sulphur. The matte is then granulated and roasted in a furance in a fluidized bed, this being accompanied by the liberation of sulphuric gases to be utilized for the production of sulphur acid. The resultant iron concentrate may contain up to 67% by weight of iron.
However, the aforedescribed method fails to provide for the recovery of nonferrous, rare and noble metals. It is only suitable for the treatment of pyrite concentrate high in sulphur.
There is a known method for treating pyrite concentrates less rich in sulphur and iron, containing 38.5% by weight of iron, 39.1% by weight of sulphur and 20% by weight of gangue. This method comprises an oxidizing roasting of the initial material, carried out in a furance in a fluidized bed at a temperature of 965.degree. C. The resultant roast is then subjected to a reducing magnetizing roasting at a temperature of 550.degree. to 650.degree. C., followed by magnetic separation thereof. The oxidized roast undergoes magnetic separation at a magnetic field intensity of 100 to 600 oersted. The resultant magnetic product undergoes pelletizing and firing, whereafter it contains up to 66% by weight of iron, thus being rendered suitable for blast-furnace smelting.
This method also fails to provide for the recovery of nonferrous, rare and noble metals.
Recovery of nonferrous and noble metals from pyrite concentrates is effected by means of oxidizing roasting of initial material in a furnaces in a fluidized bed at a temperature of 900.degree. C. The resultant gases are used for the production of sulphuric acid, and the oxidized roast is granulated in 40% solution of calcium chloride to be thereafter subjected to secondary roasting conducted at a temperature of 1250.degree. C. in cylindrical rotary kilns. The resultant iron-containing product is employed in blast furnaces. The gases evolved in the process of secondary roasting contain chlorides of nonferrous and noble metals.
The above-described method, however, includes two-stage roasting of high-grade pyrite concentrates, effected at high temperatures, which substantially increases the operating costs.
Another known method used for the recovery of nonferrous and noble metals from polymetallic material comprises subjecting this material to oxidizing roasting, which is effected in a furnace in fluidized bed at a temperature of 704.degree. to 816.degree. C. until pyrrhotine is obtained. The pyrrhotine is then subjected to aqueous lixiviation in an autoclave, with oxygen under pressure being fed therein. The nonferrous metals are passing to a solution from which they are further precipitated by means of hydrogen sulphide.
However, the roasting procedure combined with autoclave lixiviation and subsequent hydrometallurgical recovery of nonferrous metals renders the above method cumbersome and complicated.
Various techniques employed today in the treatment of rebellious polymetallic ores, notwithstanding numerous modifications and improvements, fail to satisfy growing demands of nonferrous metallurgy in high-grade selective concentrates. Thus, the increase of total volume of pyritous polymetallic concentrates, intermediary products and tails makes it absolutely necessary and essential to develop effective and comprehensive methods of treating these types for materials to yield valuable products, such as elemental sulphur, iron-ore pellets and concentrates of nonferrous metals.